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JAMB Physics 2009 Question 17

Question 17

Density and Upthrust

A plastic sphere floats in water with 50% of its volume submerged. If it floats in glycerine with 40% of its volume submerged, the density of the glycerine is [density of water = 1000 kgm−3]

  1. A.1400 kgm−3.
  2. B.1250 kgm−3.
  3. C.500 kgm−3.
  4. D.1000 kgm−3.
Show the answer and explanation

Answer: B (1250 kgm−3.)

Explanation

The upthrust equals the same weight in both liquids: 1000 × 0.5V = ρ × 0.4V, so ρ = 500 ÷ 0.4 = 1250 kg m−3.